1. Field of the Invention
The present invention relates to a ball joint and is particularly directed to a ball joint wherein load is principaly applied in the direction parallel to the shank of the ball stud with the ball stud and the socket rotating relative to each other.
2. Description of the Prior Art
According to conventional ball joints used for a rack and pinion type steering system for automotive vehicles, the main load is applied in the direction parallel to the shank portion of the ball stud, with either the ball stud or the socket rotating. A known example of such type of ball joint is described in Japanese Utility Model Publication No. 27085/1985.
The above conventional ball joint comprises a ball stud provided with a ball bearing around the end of the shank portion thereof to rotatably support a head member which has a spherical outer surface and is contained inside a socket with a ball seat in between. Such conventional ball joint is further characterized by either the shank portion of the ball stud or the socket being connected to the rack bar side of the steering mechanism of an automobile to be moved and rotated in the direction parallel to the rack bar and that the other is connected to the tie rod at the wheel side and interlocked with the said movements in the direction parallel to the rack.
At the time of assembling such a conventional ball joint, preload is applied to the head member with a ball seat made of elastic synthetic resin in order to compensate for abrasion of the contact surface between the ball seat and the head member, but, in this way, the ball bearing does not receive sufficient preload.
In other words, preload such as above is applied to a certain extent to the raceway in which the balls roll, but when the raceway has been worn with abrasion, it will produce play around the ball stud in the direction of its shank center. And wear of the ball stud in the direction of the shank portion center is fatal to the functioning of this type of ball joint. Therefore means to compensate for abrasion is necessary.